Baiji's demise holds conservation lessons

19 November 2010

The extinction of the baiji, the freshwater dolphin that once roamed China's Yangtze River, may point towards important flaws in how conservation biologists assess which species are at risk of disappearing.

The dolphin was probably doomed by a combination of legal and illegal overfishing, heavy river traffic and pollution from farms, homes and industry. Some 10 per cent of the world's population lives and works along the Yangtze, and the baiji has been among the losers in China's swift economic development.

A team led by Dr Samuel Turvey of the Institute of Zoology, Zoological Society of London, travelled to China and interviewed around 600 fishermen on the Yangtze, asking questions about when and where they last saw a baiji.

'The problem is that by definition before species go extinct, they become very rare and hard to find. This means we don't have good information about the dynamics of species decline,' Turvey comments. 'But fishermen spend their whole working lives on the river, and we realised that we could use interviews with them not just for information on the baiji but also more general conservation biology data about how extinction happens.'

These interviews didn't just add to the growing conviction that the baiji is gone forever; they suggested that it didn't die out in the way currently accepted theories suggest it should have.

'It was very disconcerting how quickly people seem to have forgotten about these animals. We'd expected that there would still be memory among fishing communities of what the river used to be like, but that knowledge is disappearing fast.'Dr Samuel Turvey, Institute of Zoology

Prevailing theories of extinction suggest that two things happen as a species dies out; the number of individuals drops, and the area they inhabit – the species' range – shrinks and ultimately fragments as the doomed creatures retreat into 'refugia', small pockets of habitat where conditions remain favourable. This breaks the population into isolated groups that can't reach each other to reproduce, hastening extinction.

But the baiji's demise doesn't seem to have unfolded this way. Right up until the end, fishermen were spotting baiji throughout their former range, which stretched much of the way up the Yangtze - one of the world's longest rivers. The number of animals was plummeting but their range seemed unaffected until they disappeared for good.

Turvey thinks that with very mobile or migratory animals, contraction of range may not always come before extinction. Another example is the slender-billed curlew – only a handful of these birds may still survive, but these survivors still migrate over a huge area of Eurasia and Africa. 'Range collapse is a bad sign, but it's not necessary for extinction – even without it, a population could still be under threat,' he says.

He argues that interviews with locals, even if they aren't trained observers of wildlife, are a valuable and underused resource for conservationists. The information they gather has its shortcomings, but it can help when official data is inadequate or nonexistent. Records of the state of the Yangtze's fisheries from the 1960s and '70s aren't reliable, since local officials under the communist regime had strong incentives to embellish the facts and present the situation as better than it really was.

Turvey is now preparing a similar research programme in Bangladesh to interview locals about their experiences of the Ganges River dolphin, which is in steep decline but not yet critically threatened.

Gone, and being forgotten

It's not absolutely certain that the baiji is completely extinct, but Turvey is sure no viable breeding population is left. When he conducted a survey of the Yangtze in 2007, using trained observers and sonar, he found no sign of baiji anywhere.

Efforts to protect the dolphins proved ineffective. The Chinese government did designate some stretches of river as protected zones, but it was never clear how the animals were supposed to know they should stay in them. Rules limiting fishing in these zones weren't enforced, and boats continued to move through and kill baiji in collisions.

The best hope for saving the baiji was to remove some of them and set up a breeding population elsewhere, but this didn't happen either. A few lone individuals were kept in captivity, and there were proposals to set up a sanctuary in an oxbow lake that had become cut off from the main river channel – effectively the Yangtze ecosystem without much of the pollution and ship traffic. But these plans were never carried out, and no two baiji of breeding age were ever kept together.

The baiji is only the best-known Yangtze species to die out in recent years. The huge Chinese paddlefish, the biggest freshwater fish in the world, is now also believed to be effectively extinct too.

Fisherman being interviewed.

As well as facing the same problems of river traffic, heavy fishing and pollution, paddlefish migrated out to sea to breed and then back up the river to spawn, and the construction of hydroelectric dams prevented this movement. There may be a paddlefish or two swimming about somewhere in the river system, but there is almost certainly no viable breeding population left.

Turvey had hoped that the baiji's demise would spur efforts to conserve other species. The signs aren't entirely encouraging, though. The paddlefish is already dead, and he is now also concerned about the fate of the Yangtze's unique freshwater population of finless porpoises.

These are still relatively numerous – a recent survey estimated around 1100 individuals – but they are disappearing fast; this is around half the number seen in the 1990s. Fishermen continue to use the illegal rolling hook long-line techniques that almost certainly helped kill the baiji. The porpoises are showing signs of range fragmentation, unlike the baiji, though more research is needed to understand why.

Another recent paper by the team draws on the same set of interviews to suggest locals' memories of the baiji, and of other unique Yangtze species like the paddlefish, are already fading.

Far from serving as a stark warning of how easy it is to lose the unique results of millions of years of evolution, these majestic animals are quickly disappearing from memory. Some 70 per cent of interviewees under 40 or who became fishermen after 1995 had no knowledge of the paddlefish, for example. These are big, memorable creatures, but once people stop seeing them regularly they disappear from memory with disturbing speed.

'It was very disconcerting how quickly people seem to have forgotten about these animals,' Turvey comments. 'We'd expected that there would still be memory among fishing communities of what the river used to be like, but we found that knowledge is disappearing fast.'

'Even if younger people hadn't seen a baiji themselves, we thought they'd have been told about them by the older fishermen,' he adds. 'But we could be sitting talking to one of the elders about when they used to see baiji, and their 40-year old son sitting next to them wouldn't have any idea what we were talking about.'

Spatial and temporal extinction dynamics in a freshwater cetacean. Proceedings of the Royal Society B (2010) 277:1697,3139-3147. DOI: 10.1098/rspb.2010.0584